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*''E. coli'' is part of the flora of the large intestine, but is not usually found in the small intestine
 
*''E. coli'' is part of the flora of the large intestine, but is not usually found in the small intestine
 
*Some strains possess fimbrae which attach the bacteria to the small intestinal epithelium of particular animal species
 
*Some strains possess fimbrae which attach the bacteria to the small intestinal epithelium of particular animal species
*''E. coli'' may cause diarrhoea via attaching and effacing lesions, where bacteria adhere intimately to the enterocyte, and cause localised effacement of the brush border microvilli; the epithelial erosion causes dysentery
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*''E. coli'' may cause diarrhoea via attaching and effacing lesions, where bacteria adhere intimately to the enterocyte, and cause localised effacement of the brush border microvilli; the epithelial erosion causes [[General Pathology - Haemorrhage|Dysentery|dysentery]]
*Enterotoxigenic ''E. coli'' (ETEC):
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*'''Enterotoxigenic ''E. coli'' (ETEC)''':
 
**General:
 
**General:
 
*** Contributes to [[Intestines - Catarrhal Enteritis#Undifferentiated Neonatal Calf Diarrhoea|undifferentiated neonatal calf diarrhoea]], a mixed viral enteritis in calves, also known as enteric colibacillosis
 
*** Contributes to [[Intestines - Catarrhal Enteritis#Undifferentiated Neonatal Calf Diarrhoea|undifferentiated neonatal calf diarrhoea]], a mixed viral enteritis in calves, also known as enteric colibacillosis
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***K88 (F4) is associated with adhesion to the small intestinal mucosa of pigs
 
***K88 (F4) is associated with adhesion to the small intestinal mucosa of pigs
 
***K99 (F5) associated with adhesion in pigs and cattle (these fimbrial adhesins were originally thought to be capsular (K) antigens)
 
***K99 (F5) associated with adhesion in pigs and cattle (these fimbrial adhesins were originally thought to be capsular (K) antigens)
***The fimbriae are encoded by plasmids
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***The '''fimbriae are encoded by plasmids'''
 
***These strains carry a plasmid which encodes an enterotoxin
 
***These strains carry a plasmid which encodes an enterotoxin
***Two types of enterotoxin: heat-labile (LT) and heat-stable (ST) toxins
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***Two types of '''enterotoxin: heat-labile (LT) and heat-stable (ST) toxins'''
***The plasmids which produce these toxins are responsible for the pathogenicity of these strains
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***The '''plasmids''' which produce these toxins are '''responsible for the pathogenicity''' of these strains
***LT is an oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer)
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****'''LT'''
***It attaches to the brush border of the epithelial cells of the small intestine
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*****An oligometric toxin composed of an enzymatically-active A subunit (30KDa; 2 fragments - A1 and A2) and 5 identical B subunits (12KDa) forming the binding portion (B oligomer)
***LT causes ADP-ribosylation of the stimulatory subunit of guanine nucleotide binding proteins of the adenylate cyclase complex in eukaryotic cell membranes
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*****It attaches to the brush border of the epithelial cells of the small intestine
***This causes irreversible activation of adenylate cyclase in target cells
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*****Causes ADP-ribosylation of the stimulatory subunit of guanine nucleotide binding proteins of the adenylate cyclase complex in eukaryotic cell membranes
***This raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium
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*****This causes irreversible activation of adenylate cyclase in target cells
***ST activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion
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*****This raises the cAMP level and causes hypersecretion of water and chloride ions into the lumen of the small intestine and inhibits reabsorption of sodium
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****'''ST'''
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*****Activates guanylate cyclase in enteric epithelial cells, stimulating fluid secretion
 
**Clinical signs:
 
**Clinical signs:
 
***The gut becomes distended with fluid and a [[Intestines - diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]] which lasts several days results
 
***The gut becomes distended with fluid and a [[Intestines - diarrhoea#Secretory Diarrhoeas|secretory diarrhoea]] which lasts several days results
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